The experimental work presented in this thesis explores, in anaesthetized and mid-collicular decerebrate, unanesthetized, cats, the properties of two components of the discharge of sympathetic nerves which are time-locked to the central respiratory cycle and are presumably generated within the central nervous system. One is the inspiration-synchronous burst, the other is a previously unknown late-expiratory burst. The properties of the inspiration-synchronous burst and its temporal relation to the phrenic nerve burst were studied under conditions in which the frequency of the latter was changed over a wide range by superior laryngeal nerve stimulation, by changes in ventilation frequency while the phrenic nerve burst was locked to the pump, and by hypocapnic hyperthermia. The data obtained are consistent with the hypothesis of a common rhythmic driver for phrenic motoneurons and sympathetic preganglionic neurons. Stimulation of low-threshold afferents in the superior laryngeal nerve selectively suppressed the phrenic burst together with the inspiration-synchronous sympathetic discharge and produced vasodilatation. The contribution of the inspiration-synchronous sympathetic discharge to neurogenic vasoconstriction was estimated, in the hindlimb of the cat, from the magnitude of the vasodilatation. A late-expiratory burst of sympathetic discharge was produced by systemic hypercapnia and by raising end-expiratory pressure to between 2 and 7 cmH$ sb2$O. Circumstantial evidence suggests this late-expiratory burst is due to input from late-expiratory neurons to sympathetic preganglionic neurons. As a background to the experimental data a survey is presented of present knowledge of the mechanisms providing mechanical and neural coupling between respiration and circulation. The functional significance of respiratory modulation of sympathetic activity is discussed.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.75943 |
| Date | January 1988 |
| Creators | Bachoo, Manjit |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 000910312, proquestno: AAINL52385, Theses scanned by UMI/ProQuest. |
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